Measles resets children’s immune systems to a “baby-like” state

Measles resets children’s immune systems to a “baby-like” state

New studies have shown that measles can compromise the immune system’s ability to fight off other infections for months or even years by causing “immune amnesia.”

Two studies involving unvaccinated Dutch children found measles makes the body “forget” the immunity it had developed and “resets” the immune system to a baby-like state.

The baby-like immune system cannot fight off other pathogens

Babies start making a narrow range of antibodies that becomes more varied as they grow older.

"The measles virus removed immune memory cells that are created in response to other pathogens they had seen before,” says study leader Velislava Petrova from the Wellcome Sanger Institute in Hinxton, U.K. “They also returned the immune system back to a baby-like state where they have limited ability to respond to new pathogens.”

The findings are particularly relevant given the sharp increase in the incidence of measles which was 30% higher in 2018 compared with 2017 due to under vaccination.

"If we allow [measles] outbreaks to happen, we are knowingly creating pockets of people who are susceptible to other diseases as well," warns Petrova.

"These two studies provide further strong evidence for the highly immunosuppressive effects of measles infection and the power of measles vaccination to counter it," adds population biologist Bryan Grenfell of Princeton University, who was not involved in the study.

The findings come from a detailed analysis of population data available for children from an Orthodox Protestant community in the Netherlands whose parents had chosen not to vaccinate their children for religious reasons.

Researchers in the United States, UK, and the Netherlands analyzed the samples to assess the effects measles had on the immune system, with a focus on antibodies and the white blood cells that produce them.

Researchers used their newly developed VirSCan technology

Stephen Elledge and colleagues at Harvard University used a technology they have developed called VirSCan to test antibodies in the children’s blood against most known human pathogenic viruses. This enabled the team to create an extremely detailed picture of the children’s immune systems before and after they had become infected with measles.

"Measles is like the first 10 years of an untreated HIV infection compressed into a few weeks”

As reported in the journal Science, measles caused the children to lose an average of 20% of their antibody repertoire. One child, who had a severe infection, lost 73% of this repertoire.

This effect was not seen in a control group made up of five vaccinated children who did not contract measles over the course of the study, as well as more than 100 other children and adults.

Measles is like the first 10 years of an untreated HIV infection compressed into a few weeks - that's the kind of immunological memory damage,"
Harvard virologist and co-author Michael Mina
Before the children contracted measles, their blood contained antibodies that target many common pathogens. "These were really healthy kids," adds Mina.

The depleted repertoire of antibodies means children become vulnerable again to viruses they had been exposed to and developed immunity to in the past. "It's like taking somebody's immune system and rewinding time, putting them at a more naïve state," Mina warns.

Measles deletes existing immune memory and prevents future immunity

To understand the effect, Petrova's group conducted another analysis of the children’s blood. They looked at B cells, which “remember” previous infections and which the measles virus is known to infect.

As reported in the journal Science Immunology, measles infection reduced the diversity of memory B cells. It killed off B cells specific to pathogens other than measles and replaced them with new measles-specific memory B cells.

Measles also reduced the diversity of nonspecific naïve B cells in the bone marrow, which stand ready to combat unknown infections. Measles left this category of B cells "immature, similar to that of a fetus," says Petrova.

In other words, measles not only deletes immune memory, but it also makes it more difficult for the immune system to fight off newly encountered pathogens in the future.

Mina stressed that the only way to prevent measles from erasing immune memory is to prevent cases by vaccinating.

The studies were “elegant and thorough”

President of the British Society for Immunology, Arne Akbar, said the studies were elegant and thorough: "It is doubly important to make sure you and your children are vaccinated against measles.”

With vaccination rates in the UK falling and recently losing our measles-free status, an outbreak is now a ticking time bomb.”
Liam Sollis, Unicef UK

"Vaccines are the safest and most effective preventative measures against highly infectious disease," he concludes.

Journal references:
Petrova, V.N. et al. (2019) Incomplete genetic reconstitution of B cell pools contributes to prolonged immunosuppression after measles
DOI: 10.1126/sciimmunol.aay6125

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